Effects of annealing temperature on the microstructure and hardness of TiAlSiN hard coatings

TiAlSiN hard coatings were synthesized on high-speed steel using an arc ion enhanced magnetic sputtering hybrid system.The microstructure and hardness of the coatings at different annealing temperatures were explored by means of XRD,TEM,EDAX and Vickers indentation.The as-deposited TiAlSiN coatings were confirmed to be amorphous due to high depositing rate and low deposition temperature during the film growth.The transformation from amorphous to nanocomposites of nano-crystallites and amorphousness were observed after the annealing treatment,the microstructure of TiAlSiN coatings annealed at 800°C and 1000°C were consisted of crystalline hcp-AlN,fcc-TiN and amorphous phase,however,the coatings were only consisted of fcc-TiN and amorphous phase when annealing at 1100°C and 1200°C.Meanwhile,the formation of Al2O3 was detected on the coating surface after annealing at 1200°C and it indicated the excellent oxidation resistance of the TiAlSiN coatings under the present experimental conditions.Furthermore,the average grain size of the TiAlSiN coatings after high temperature annealing even at 1200°C was less than 30 nm and the size increased with the increasing temperature.However,the hardness of the so-deposited coatings with HV0.2N=3300 dramatically decreased with the increase of temperature and reached nearly to the hardness of TiN coatings with HV0.2N=2300.     

Hot compression deformation behavior of AISI 321 austenitic stainless steel

The hot compression behavior of AISI 321 austenitic stainless steel was studied at the temperatures of 950–1100℃ and the strain rates of 0.01–1 s?1 using a Baehr DIL-805 deformation dilatometer. The hot deformation equations and the relationship between hot deformation parameters were obtained. It is found that strain rate and deformation temperature significantly influence the flow stress behavior of the steel. The work hardening rate and the peak value of flow stress increase with the decrease of deformation temperature and the increase of strain rate. In addition, the activation energy of deformation (Q) is calculated as 433.343 kJ/mol. The microstructural evolution during deformation indicates that, at the temperature of 950℃ and the strain rate of 0.01 s?1, small circle-like precipitates form along grain boundaries; but at the temperatures above 950℃, the dissolution of such precipitates occurs. Energy-dispersive X-ray analyses indicate that the precipitates are complex carbides of Cr, Fe, Mn, Ni, and Ti.     

Microstructural evolution of a superaustenitic stainless steel during a two-step deformation process

Single- and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150℃ and at a strain rate of 0.1 s-1. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050℃. However, the gentle static softening at 1100 and 1150℃ was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.     

Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quenching temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the temperature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M₂₃C₆ existing in the matrix of the quenched steel.     

Grain boundary characteristics and tensile properties of Ti14 alloy after semi-solid deformation

The microstructure and room-temperature tensile properties of Ti14, a new α+Ti₂Cu alloy, were investigated after conventional forging at 950℃ and semi-solid forging at 1000 and 1050℃, respectively. Results show that coarse grains and grain boundaries are obtained in the semi-solid alloys. The coarse grain boundaries are attributed to Ti₂Cu phase precipitations occurred on the grain boundaries during the solidification. It is found that more Ti₂Cu phase precipitates on the grain boundaries at a higher semi-solid forging temperature, which forms precipitated zones and coarsens the grain boundaries. Tensile tests exhibit high strength and low ductility for the semi-solid forged alloys, especially after forging at 1000℃. Fracture analysis reveals the evidence of ductile failure mechanisms for the conventional forged alloy and cleavage fracture mechanisms for the alloy after semi-solid forging at 1050℃.     

In situ observations of austenite grain growth in Fe-C-Mn-Si super bainitic steel

In situ observations of austenite grain growth in Fe-C-Mn-Si super bainitic steel were conducted on a high-temperature laser scanning confocal microscope during continuous heating and subsequent isothermal holding at 850, 1000, and 1100℃ for 30 min. A grain growth model was proposed based on experimental results. It is indicated that the austenite grain size increases with austenitizing temperature and holding time. When the austenitizing temperature is above 1100℃, the austenite grains grow rapidly, and abnormal austenite grains occur. In addition, the effect of heating rate on austenite grain growth was investigated, and the relation between austenite grains and bainite morphology after bainitic transformations was also discussed.     

Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing

Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing was investigated by optical microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that crystallographic slip was the predominant deformation mechanism in the early stage of deformation. Deformation twins started to form when the rolling reduction was larger than 38.9%; both the dislocation density and the number of twins increased with increasing rolling reduction. The initial texture of the Zr 702 plate consisted of the basal fiber component. During cold rolling the strength of the basal fiber first decreased and then increased with increasing rolling reduction. The cold-rolled sheets were fully recrystallized after being annealed at 550°C. The recrystallization temperature and the size of recrystallized grains decreased with increasing rolling reduction. A larger rolling reduction resulted in a higher grain growth rate when the annealing temperature increased from 550°C to 700°C. The recrystallization texture was characterized by a major basal fiber and a minor {0113}<2110> component. The strength of the recrystallization texture increased with increasing rolling reduction.     

Effect of decarburization annealing temperature and time on the carbon content,microstructure, and texture of grain-oriented pure iron

In this study, the effect of decarburization annealing temperature and time on the carbon content, microstructure, and texture of grain-oriented pure iron was investigated by optical microscopy and scanning electron microscopy with electron-backscatter diffraction. The results showed that the efficiency of decarburization dramatically increased with increasing decarburization temperature. However, when the annealing temperature was increased to 825℃ and 850℃, the steel's carbon content remained essentially unchanged at 0.002%. With increasing decarburization time, the steel's carbon content generally decreased. When both the decarburization temperature and time were increased further, the average grain size dramatically increased and the number of fine grains decreased; meanwhile, some relatively larger grains developed. The main texture types of the decarburized sheets were approximately the same:{001}<110> and {112~115}<110>, with a γ-fiber texture. Furthermore, little change was observed in the texture. Compared with the experimental sheets, the texture of the cold-rolled sheet was very scattered. The best average magnetic induction (B₈₀₀) among the final products was 1.946 T.     

Austenite grain growth behavior of Q1030 high strength welded steel

The austenite grain growth behavior of Q1030 steel was studied under different heating conditions. The austenite grain size increases with the heating temperature and holding time increasing. Austenite grains grow in an exponential manner with rising heating temperature and in a parabolic manner with prolonging holding time. A mathematical model for describing the austenite grain growth behavior of Q1030 steel was obtained on the basis of experimental results using regression analysis. When the heating temperatures lie between 1000 and 1100℃ at a certain holding time, abnormal grain growth appears, which causes mixed grains in Q1030 steel.     

Grain size effect of IrO2 nanocatalysts for the oxygen evolution reaction

Combined with air annealing, rutile-structured IrO 2 nanoparticles with various sizes were prepared using colloidal method. The nanoparticles were used as the electrocatalysts for the oxygen evolution reaction (OER) in acidic media, and their grain size effect was studied. The results show that with the increase in annealing temperature, the grain size of the catalyst increases, and the voltammetric charges (the electroactive areas) and apparent activity for the OER decrease. The relationship between the intrinsic activity and the annealing temperature exhibits a volcano-type curve and the catalyst annealed at 550 ℃ achieved the best result.     

Improved strength and ductility of high alloy containing Al-12Zn-3Mg-2.5Cu alloy by combining non-isothermal step rolling and cold rolling

Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of α-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room temperature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects (e.g., dislocations, stacking faults, and sub-grains). The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.     

Effect of annealing temperature on CrN microspheres synthesized by CAP technology

CrN microspheres were synthesized by using a cathodic arc plasma source system. The obtained samples were annealed in air at temperatures of 300-800 ℃ for 60 min. The influence of annealing temperature on the microstructure and surface morphology of the CrN microspheres was investigated. The CrN microspheres were characterized by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. The results show that the CrN nanoparticles arranged into leaf-like structures before annealing. With the rising of the annealing temperature, the size of CrN crystal nanoparticals became larger. When the annealing temperature exceeded the oxidation point(500 ℃), the CrN was oxidized and the leaf-like structure was broken. With further increase of the annealing temperature(700 ℃), the arrangement of CrN nanoparticles was changed from leaf-like structure to be discrete.     

The formation and stability of Si1-x C x alloys in Si implanted with carbon ions

Si_1-xC_x alloys of carbon (C) concentration between 0.6%—1.0% were grown in Si by ion implantation and high temperature annealing. The formation of Si_1-xC_x alloys under different ion doses and their stability during annealing were studied. If the implanted dose was less than that for amorphizing Si crystals, the implanted C atoms would like to combine with defects produced during implantation and it was difficult to form Si_1-xC_x alloys after being annealed at 850℃. With the increment of implanted C ion doses, the lattice damage increased and it was easier to form Si_1-xC_x alloys. But the lattice strain would become saturate and only part of implanted carbon atoms would occupy the substitutional positions to form Si_1-xC_x alloys as the implanted carbon dose increased to a certain degree. Once Si_1-xC_x alloys were formed, they were stable at 950℃, but part of their strain would release as the annealing temperature increased to 1 000℃. Stability of the alloys became worse with the increment of carbon concentration in the alloys.     

退火温度对含磷高强IF钢FeTiP析出行为的影响

通过模拟罩式退火过程,研究了含磷高强IF钢中FeTiP粒子在退火过程中的析出行为,利用透射电镜选区衍射并结合能谱分析,确定了FeTiP的晶体结构.结果表明:650℃退火试样中只含有少量FeTiP,随着退火温度的升高,FeTiP数量明显增加,其大量分布于晶内及晶界处,且晶界处析出物尺寸明显大于晶内析出物.当退火温度升高到800℃时,FeTiP完全溶解,因此在整个基体无法检测到FeTiP.FeTiP的溶解消除了其对再结晶的阻碍作用,最终获得高强度{111}取向再结晶组织,从而提高高强IF钢成形的性能.FeTiP具有斜方晶体结构,且析出物中Nb元素的存在(含Nb原子可表达为Fe(Ti,Nb)P)不会引起晶体结构的改变.     

Effect of temper rolling on the bake-hardening behavior of low carbon steel

In a typical process, low carbon steel was annealed at two different temperatures (660℃ and 750℃), and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subsequently carried out to measure the bake-hardening (BH) values. The influences of annealing temperature and temper rolling on the BH behavior of the steel were investigated. The results indicated that the microstructure evolution during temper rolling was related to carbon atoms and dislocations. After an apparent increase, the BH value of the steel significantly decreased when the temper rolling reduction was increased from 0% to 5%. This was attributed to the increase in solute carbon concentration and dislocation density. The maximum BH values of the steel annealed at 660℃ and 750℃ were 80 MPa and 89 MPa at the reductions of 3% and 4%, respectively. Moreover, increasing the annealing temperature from 660 to 750℃ resulted in an obvious increase in the BH value due to carbide dissolution.     

Modulation structure stability of heat-treated Co/C and CoN/CN soft X-ray multilayers

Modulation structure stability of Co/C and CoN/CN soft X ray multilayers has been investigated by X ray diffraction and Raman spectroscopy. The graphitization of the amorphous carbon layers in Co/C multilayers causes a period expansion of 12% at annealing temperatures below 400℃. An enormous period expansion (～40%) induced by the crystallization and agglomeration of Co layers has been observed at 500℃. While the period expansion of CoN/CN multilayers is only 4% at 400℃. The interface pattern of the CoN/CN multilayers still exists even if they were annealed at 700℃. The relatively good thermal stability of CoN/CN multilayers can be attributed to the suppression of the formation of the sp 3 bonding and, at annealing temperatures higher than the phase transition temperature of 420℃ (from hcp to fcc), the coexistence of hcp and fcc Co structures through doping nitrogen.     

冷轧工艺对取向硅钢初次再结晶织构的影响

研究了取向硅钢制备过程中常见的两种冷轧工艺,主要研究了一阶段冷轧与两阶段冷轧+中间退火工艺对初次再结晶组织及织构的影响.结果表明:采用两阶段冷轧+中间退火工艺制备以Cu2S为主抑制剂的取向硅钢,其初次再结晶平均晶粒尺寸为181μm,高斯晶粒的体积分数为06%,迁移性强的重位点阵晶界(Σ5+Σ9)和高能晶界(20°~45°取向偏差角)所占比例分别为18%和504%.与一阶段冷轧工艺相比,其初次再结晶晶粒较细,且高斯晶核与特征晶界所占的比例较高,有利于高斯晶粒发生二次再结晶.     

Ag/FePt/C薄膜的结构和磁性

采用直流和射频磁控溅射在Si(001)基片上制备Ag/FePt/C薄膜,并将其在不同温度下进行真空热处理,得到了具有高矫顽力的L10-FePt薄膜.利用X射线荧光(XRF)、X射线衍射(XRD)和振动样品磁强计(VSM)研究样品的成分、结构和磁性.结果表明,样品经400℃热处理后发生了无序—有序相转变,以Ag元素为底层可降低有序化温度,添加Ag和C可抑制晶粒生长.随着热处理温度的升高,FePt的晶粒尺寸和矫顽力逐渐增大,经600℃热处理后,样品中FePt的平均晶粒尺寸为14nm,垂直膜面和平行膜面的矫顽力分别为798.16kA/m和762.35kA/m.     

退火温度对超纯Cr17铁素体不锈钢冷轧板成形性能的影响

对一种铌、钛双稳定化的超纯Cr17铁素体不锈钢的冷轧板进行不同温度的退火实验,探讨了对组织、织构及成形性能的影响.研究结果表明,退火温度是影响成形性能的关键因素.随着退火温度的升高,晶粒的平均尺寸逐渐增大,不均匀化程度逐渐加重.并且,γ纤维织构逐渐增强,α纤维织构逐渐减弱,使-r值逐渐增大,而Δr值变化不大.为了防止"橘皮"缺陷的产生,退火温度应低于1 000℃,平均晶粒尺寸应控制在40μm以下.在保证不产生"橘皮"缺陷的前提下,试验钢的冷轧板经975℃退火后具有最佳的成形性能:-r值高达1.92,Δr值仅为0.12.     

Mo离子注入钢退火过程中的相变研究

着重研究了金属离子注入合成表面优化复合层的机理和纳米相镶嵌结构形成,探索了注入和退火过程中纳米结构和相变过程,讨论相变机制.实验中发现用较低束流密度的Mo离子注入钢明显地改变了钢表面的结构,可使钢表面晶粒细化,使阻止位错移动的晶界数量增多;可在钢表面形成Mo原子超饱和固溶体;随所用的束流密度的增加,注入时表面温度升高,注入的Mo原子将与钢中的铁原子和碳原子化合而形成纳米尺寸的析出相.这些弥散的析出相在钢表面形成了弥散强化.用低束流密度注入后经过退火,在钢表面也形成了纳米尺寸的析出相,从而增加了表面弥散强化的效果.随退火温度的增高,纳米析出相将会聚成大一些的纳米颗粒,颗粒之间互相连接而形成网状结构,这将会进一步增加表面强化效果.